Abstract: A four-stroke internal combustion engine includes a cylinder block including a cylinder therein and having a piston reciprocally disposed within the cylinder. A piston is operably engaged with a crankshaft. At least one intake valve is reciprocally driven by a camshaft. At least one exhaust valve is reciprocally driven by the camshaft. A vacuum release mechanism includes an operating member reciprocally supported within the camshaft for translation along an axis. A centrifugally actuated flyweight member is engaged with the operating member, wherein rotation of the camshaft above engine cranking speeds causes the flyweight member to move the operating member from a first position to a second position. A vacuum release member is movably supported within the camshaft and is in engagement with the operating member wherein translational movement of the operating member causes movement of the vacuum release member.

Abstract: A four-stroke internal combustion engine includes a cylinder block including a cylinder therein and having a piston reciprocally disposed within the cylinder. A piston is operably engaged with a crankshaft. At least one intake valve is reciprocally driven by a camshaft. At least one exhaust valve is reciprocally driven by the camshaft. A vacuum release mechanism includes an operating member reciprocally supported within the camshaft for translation along an axis. A centrifugally actuated flyweight member is engaged with the operating member, wherein rotation of the camshaft above engine cranking speeds causes the flyweight member to move the operating member from a first position to a second position. A vacuum release member is movably supported within the camshaft and is in engagement with the operating member wherein translational movement of the operating member causes movement of the vacuum release member.

Abstract: A four-stroke internal combustion engine includes a cylinder block having a cylinder therein and a piston reciprocally disposed within the cylinder. The piston is operably engaged with a crankshaft. At least one intake valve and one exhaust valve is reciprocally driven by a camshaft. A vacuum release mechanism includes an operating member rotationally supported by the camshaft and has an operator disposed thereon. A centrifugally actuated flyweight member is attached to the operating member, wherein rotation of the camshaft above engine cranking speeds causes the flyweight member to rotate the operating member. A vacuum release member is reciprocally supported by the camshaft and in engagement with the operator wherein rotational movement of the operating member causes radial translation of the vacuum release member through the operator.